ATLANTA (Reuters) - A 40 percent decline in the death rate of diabetic American adults from heart disease and strokes is a sign that patients are taking better care of themselves and receiving improved treatment, according to a government study released on Tuesday.

"Diabetes leads to many complications and shorter life spans," Edward Gregg, the study's lead author and chief of epidemiology and statistics in CDC's Division of Diabetes Translation, told Reuters on Tuesday.

"The fact that we found substantially lower death rates in both men and women was very encouraging," he said.

Diabetics are less likely to smoke than in the past and more likely to be physically active, the CDC said, although it noted that obesity levels among diabetics continues to rise. Better control of high blood pressure and high cholesterol may also have contributed to the decline in death rates among diabetics, it said.

"When you see an effect on mortality like this, it's not due to one factor, it's really all those factors," said Gregg.

The study examined data from 250,000 patients.

Despite the significant decline in diabetic deaths from cardiovascular disease, the rate is still twice as high as those without the disease, the CDC said.

On average, diabetes diagnosed in middle age reduces a patient's life expectancy by 10 years, although the gap likely will narrow as diabetics live longer, said Gregg.

An estimated 25.8 million people in the United States have diabetes, which is marked by high levels of glucose in the blood, the CDC said. The number of people with diabetes continues to increase, said Gregg.

Obesity is a major cause of the increase in Type 2 diabetes, which is most common in adults, he said.

"There's still a long way to go," said Gregg. "The fact that Type 2 diabetes can be prevented with lifestyle intervention means that we really need to do more."